Octavio is in love with his abusive brother's wife Susana. In an early scene, Octavio's brother becomes enraged at Susana for letting the dog out out of the house, and Octavio takes the blame for it, an act to prove his loyalty to Susana. But these attempts by Octavio put Susana into a position of disloyalty, which she does not know how to maneuver. It also makes him disloyal to his brother, and his mother who does not want Octavio to fight his brother. In order to further prove his loyalty to Susana, Octavio then uses the dog in dog fighting to acquire large amounts of cash to run away with her. The dog does exceptionally well, and Octavio's brother demands half of the winnings, claiming the dog is his. Octavio refuses. The dog parallels Susana here: who takes care of the dog? who takes care of Susana? who owns Susana? who owns the dog? On the eve of a crucial fight, Octavio comes home to find that his brother has taken Susana away. Susana stays loyal to the brother like a dog, irregardless of the pain he enacts on her. Susana is disloyal to Octavio's fantasy that he builds on the dog's success. A rival owner shoots Octavio's dog just as it is about to beat the other dog. Octavio calls him a "crazy fucker", and the linguistic choice of "crazy" is interesting to note. He has become irrational, in his love for victory, flouting the rules for reward.
The next chapter follows Spanish supermodel Valeria who is having a covert relationship with a married magazine editor Daniel. On television, she pretends to be in a relationship with fellow celebrity and introduces their "son", her dog Richie. To protect Daniel, she risks her career. Her deception here foreshadows the events which will transpire. A car accident, caused by Octavio on the run, leaves Valeria injured and bed-ridden. Richie dives into a hole in the floorboards of the new apartment that Daniel has bought for her. The hole is a representation of Daniel's fragile loyalty to her, and her "son" disappears into his volatility. Valeria cannot get Richie out and re-injures her leg, ending her career. Her devotion to Richie and Daniel destroy her. Valeria's beloved dog is disloyal to her, but Valeria is relentlessly haunted by his whimpers at night. The missing dog and the amputation of her leg arouses tension between Daniel and Valeria, and Daniel considers returning to his wife. He finally breaks open the floor in a craze and finds Richie, which parallels Daniel's renewed loyalty to Valeria.
It is with the ex-guerilla leader El Chivo turned vagrant secret hit-man that director Innaritu really insists on the animal symbolism. He lives with several stray dogs in an abandoned warehouse and happens to be at the scene during the crash. El Chivo steals Octavio's money and takes his wounded dog to revive it. El Chivo returns one day to find all his dogs killed by Octavio's dog, due to his proclivity for dog fighting. He becomes acutely distressed and is on the verge to shoot. But he decides to forgive both the dog and himself. In the dog's violence, he seems himself and the illogical lifestyle he lives because of his unexpressed love for his daughter. El Chivo tells the dog "it's not right asshole". To kill the dogs of the man who revives it is unjustifiable. This episode precipitates a big change in El Chivo, cutting his hair and revealing to his daughter that he is alive.
Innaritu uses the animal as a representation of a human in love. He includes both the fluffy domestic dog Richie and the ferocious fighting dogs. To love makes you literally an animal, a bitch. Humans are animals when they are in love. Is this true? We do become more impulsive.There is many a story of characters coming to their demise at the hands of a seductress because they could not act intelligently like humans. Our flight/fight instincts seem to kick in. Innaritu includes both women and men to compare how they become in the state of love. But our "ability" to love, to emphatize is often deemed a human quality, different from animals..